Signal transduction via guanine nucleotide binding proteins (G proteins) is central to the function of drugs of abuse such as opioids, cannabinoids, and dopamine modulators (cocaine and amphetamine). A novel family of proteins, Regulators of G Protein Signaling - RGS Proteins, strongly suppresses signaling by inhibitory G proteins that are involved in the actions of these drugs of abuse. In particular RGS9 knock-out mice show dramatically enhanced responses to amphetamine, cocaine, and morphine. The availability of chemical modulators of RGS proteins will enhance our understanding of physiological and pharmacological roles of RGS proteins in the actions of drugs of abuse. Such RGS modulators will validate the potential of RGS proteins as a novel target of drug action and could provide compounds to serve as leads for therapeutics. We have recently devised high-throughput screens for modulators of the RGS/G1 interaction and identified two series of micromolar inhibitors of RGS4. In this project, we will: 1) evaluate the molecular mechanisms of RGS inhibition by these compound and undertake further high throughput screening for additional inhibitors or activators of RGS4 and RGS9, 2) determine structure-activity relations, define pharmacophore models, and optimize in vitro potency, cellular activity, and predicted pharmacokinetic properties of identified compounds, and 3) examine these compounds in transfected cell model systems and brain slices and optimize structures for biological activity. This project will provide the initial steps and proof of principle for medications development targeting RGS proteins - a key modulator of signaling related to drug abuse.